Inception of self-interacting dark matter with dark charge conjugation symmetry

A new understanding of the stability of self-interacting dark matter is pointed out, based on the simplest spontaneously broken Abelian U(1) gauge model with one complex scalar and one Dirac fermion. The key is the imposition of dark charge conjugation symmetry. It allows the possible existence of two stable particles: the Dirac fermion and the vector gauge boson which acts as a light mediator for the former's self-interaction. Since this light mediator does not decay, it avoids the strong cosmological constraints recently obtained for all such models where the light mediator decays into standard-model particles.